Rotary pumps with a magnetic coupling represent an important type of machine used industrially for delivering liquids. Relative to simpler rotary pumps with a floating ring seal, they have the advantage of a hermetic seal of the pumping space. This can appear to be favorable, especially for delivering aggressive or toxic liquids.
In most cases, coaxial rotating couplings with a radial arrangement of the magnets and corresponding radial magnetic active lines are used. Only this construction will be further considered below and is also the subject matter of the application.
The background of the invention will be explained below with reference to FIGS. 1-4 for solutions known to the state of the art.
All of the drawings show an axially longitudinal section through the pump. The rotational bodies sectioned here, for the most part, were shown without peripheral edges for the sake of clarity—with the exception of shafts.
For reasons of assembly and the different materials used, the component designated below as a pump housing (1) must be built, in practice, from several parts. A few of these are wetted by the pumped liquid and must be sealed accordingly, others need not be. However, for reasons of simpler representation, the pump housing (1) is here shown as one part.
A first known pump in a typical construction is shown in FIG. 1 and is advertised, e.g., in the brochure of the company WERNERT-PUMPEN GMBH D-45476 Mulheim am der Ruhr, Standard chemical pump made from plastic with magnetic coupling-model series NM Edition 687/02 (hereinafter “[1]”), incorporated herein by reference in its entirety.
In the pump housing (1′) a rotating pump blade wheel (4′) is arranged that receives the pumped liquid via the suction port (2′) and that ejects it again via the pressure port (3′) under the buildup of pressure.
The radial mounting of the pump blade wheel (4′) is realized by means of a blade wheel shaft (5′) typically in floating bearings (9′,10′) whose stationary parts are held in a bearing insert (11′). The pumped liquid provides the lubrication and cooling of the floating bearing (9′, 10′).
The axial mounting of the pump blade wheel (4′) and the other parts connected and rotating with the blade wheel are not considered in more detail here or below. Here, all that is indicated is that, in addition to a mechanical mounting with start-up disks, hydraulic active principles, which are based on pressure differences, as well as a magnetic mounting, can come into consideration.
The part of the rotating coupling that receives the torque through a separating wall typically constructed as a thin-walled, slotted pot (12′) and that transfers the torque via the blade wheel shaft (5′) to the pump blade wheel (4′) is designated as a magnetic rotor (6′). It is equipped with permanent magnets (7′) which, in turn, must be surrounded in a liquid-tight way with a cylindrical protective sleeve (8′) before the corrosive and possibly also abrasive attack of pumping liquid. Here, it is mentioned only as an aside that it may also be necessary to protect an approximately metallic, that is, ferromagnetic, magnetic rotor (6′) from corrosion, as well as the shaft (5′).
The part of the rotary coupling that receives and transfers the driving torque of the motor via the drive shaft (15′) is typically designated as the magnetic driver (13′). It is also equipped accordingly with permanent magnets (14′) that rotate in the air and that are therefore not subjected to special attack. The radial and axial bearing of the magnetic driver is realized in conventional roller bearings (16′).
FIG. 2 shows another typical construction, in particular, for smaller pumps. Such a pump is advertised, e.g., in the brochure of the company IWAKI Pumpen, Iwaki magnet-driven pumps-series MDM printed in Japan 99.11.UN (hereinafter “[2]”), incorporated herein by reference in its entirety.
In this construction, a bearing insert (11′) can be omitted cost-effectively. The pump blade wheel (4′) is integrally assembled with the magnetic rotor (6′), the permanent magnets (7′), and the protective sleeve (8′) as a single part. This rotating blade wheel-magnet rotor unit (19′) is here mounted with a floating fit on a stationary axle (17′). The axle (17′) itself is fixed on one side by means of flow ribs (18′) in the suction port (2′) and is supported on the other side in the specially shaped slotted pot (12′).
The construction described in FIGS. 1 and 2 and largely typical today (here designated as construction type A) is characterized in that the magnetic driver (13′) is arranged radially outward above the magnetic rotor (6′) lying farther inward. This construction has the advantage that the large mass moment of inertia of the outer magnetic driver (13′) counteracts the all-too-fast acceleration of the driving motor and thus the breakaway of the magnetic coupling can be prevented more favorably. In addition, this construction simplifies, in particular, a wide, axially spaced radial mounting of the pump blade wheel (4′), which is always a goal due to the large hydraulic forces within the pump.
More rare are magnetic coupling pumps with, in contrast, a radially outward magnetic rotor (6′) that are not in contact liquid and an inner lying magnetic driver (13′). Let this construction be designated as construction type B.
Such pumps of construction type B, which are described, e.g., in DE 01453760 or EP 0171514 or EP 0171515 and which are shown in FIG. 3, must be designed with care such that for fast acceleration, the magnetic coupling does not break away, which is a risk here due to the outward lying magnetic rotor (6′). In addition, the radially inwardly lying magnetic driver (13′) prevents an axially extended inner floating bearing of the blade wheel-magnetic rotor unit (19′), if the slotted pot (12′), which must face the drive side of the pump with its actual opening in construction type B, is not constructed disadvantageously twisted to the right. A realized pump of construction type B is advertised in the brochure of the company CP-Pumpen AG, CH-4800 Zofingen: Magnetic coupling pump MKP7, metallic (hereinafter “[3]”), incorporated herein by reference in its entirety and is used as a model for FIG. 3. Because here, in contrast to the construction corresponding to FIG. 2, the axle (17′) is fixed exclusively by the flow ribs (18′), the realized pump has the advantage of a continuous, thin-walled slotted pot (12′) which is loaded only with the internal pressure of the pump, but not with bearing forces, Similar to pumps constructed according to DE 01453760 or EP 0171514, according to U.S. Pat. No. 5,501,582 A and DE 298 22 717 UI, indeed, in addition to a direct radial bearing of the pump blade wheel, there is also a floating bearing on the outside of the magnetic rotor, but the radially farther inwardly lying bearing on the pump blade wheel leads to the known dry-running problems and jamming of the pump blade wheel and also high wear susceptibility and unfavorable synchronization properties of the blade wheel-magnetic rotor unit.
An important problem area in the operation of the above-mentioned magnetic pumps, which are provided with floating bearings and which use the pumped medium itself as its cooling and lubricating medium, is the near or complete absence of even this liquid. Such a lack of lubrication occurs when higher gas fractions collect in the liquid, e.g., due to cavitation in front of the pump, vortex entry, or by a sipping process. These gas fractions  collect in the radially inner hollow spaces of the pump body due to the centrifugal effect in the pump. In the conventional construction according to FIGS. 1-3 and according to U.S. Pat. No. 5,501,582 AI and also DE 298 22 717 U1, however, this is precisely the location of the floating bearings, which then dry out and which are therefore frequently destroyed. However, these solutions often remain bound to the tribology of the friction partners-paired with the attempt to reduce the friction power of the bearing for the lack of lubrication and thus to avoid thermal destruction.
A technically different and very useful way to displace, namely, the floating bearing susceptible to damage, as radially far outward as possible, the approach to the solution features a “shaft-less” magnetic pump as described in Robert Neumaier: Hermetic pumps Verlag und Bildarchiv WJBL Faragallah, 1994, ISBN-3-929682-05-2, Chapter 3.7.12 Shaft-less magnetic coupling rotary pumps, pp. 356ff (hereinafter “[4]”), incorporated herein by reference in its entirety, which is shown in FIG. 4. This construction is assigned to construction type A. Here, it is possible to achieve a shaft-less and axle-less construction, in that a section of the slotted pot (12′) is used as the stationary part (10′) of the floating bearing and the rotating part (9′) of the floating bearing is formed by a section of the protective sleeve (8′). The pump blade wheel (4′) is connected to the magnetic rotor (6′) the permanent magnet (7′) and the protective sleeve (8′) to form a hollow blade wheel-magnetic rotor unit (19′).
Nevertheless, the proposal from [4] remains technically limited. For example, the radial floating bearing of the blade wheel-magnetic rotor unit (19′) is realized in the slotted pot (12′) itself, which, however, must be constructed directly at this point as a very thin-walled component. This is also noted in [4], and therefore stable, additional start-up or emergency bearings (37′) which must always be formed disadvantageously due to the slotted pot (12′) can also not be eliminated there. Furthermore, the support of the bearing in the thin-walled slotted pot does not permit outer cooling or simple outer access, for example, for monitoring the bearing temperature or for forced flushing.
It remains to be stated that in the case of an operational interruption, e.g., due to cavitation in front of the pump, vortex entry or by a sipping process, a rotary pump is loaded with significantly increased gas fractions in the pumped liquid. These gas fractions collect due to the centrifugal effect in the pump in the radially inner hollow spaces of the pump body. For conventional magnetic coupling pumps, the floating bearings are located there, thus they dry out and therefore are frequently destroyed.